Catalytic convertor ensures fuel cells really are emissions-free

Scientists at one of Germany’s leading research organisations are developing a catalytic convertor that will treat waste gas from a new type of fuel cell that runs on ammonia. The technology will ensure that residual hydrogen and ammonia from the process are treated and that the only end products from the ground-breaking fuel cell are water and nitrogen. The catalytic convertor, being developed by Fraunhofer Institute for Microengineering and Microsystems (Fraunhofer IMM), will also optimise the process, ensuring it does not produce environmentally harmful nitrogen oxides.

Based in Mainz in Germany, Fraunhofer IMM has developed gas purification systems for ammonia fuel cells before, but not at the scale required in the ShipFC project, in which an ammonia fuel cell is to be tested on Viking Energy, a platform supply vessel (PSV) owned by Eidesvik. The PSV will be equipped with a 2-MW ammonia fuel cell, allowing it to operate for at least 3,000 hours annually on clean fuel. Following completion of that phase, the project will ramp up to qualifying much larger fuel cells for oceangoing vessels. Ultimately, the goal of the project is to demonstrate the feasibility of ammonia fuel cells for oceangoing vessels and long sea voyages.

Fuel cells have long been seen as environmentally friendly power and propulsion systems, but storing hydrogen on board a vessel is problematic.

In contrast, ‘hydrogen-enriched’ compounds, such as ammonia, can be stored relatively easily. Ammonia has other advantages too: as a carbon-free hydrogen carrier it is relatively easy and relatively inexpensive to synthesise from renewable sources.

“Hydrogen-enriched compounds, such as ammonia, can be stored relatively easily”

Fraunhofer IMM energy division director Professor Gunther Kolb explained: “Ammonia has significant advantages over hydrogen, which has to be stored at -253°C as a liquid, or at pressures of around 700 bar as a gas. Liquid ammonia can be stored at -33°C at standard pressure and +20°C at 9 bar. That makes storing it as an energy carrier much easier and more straightforward.”

In the fuel cell being developed in the ShipFC project, the process of generating electricity from ammonia starts with it being fed into a fission reactor, where it is split into nitrogen (N2) and hydrogen (H2); 75% of the gas produced consists of hydrogen. A small amount of ammonia (100 ppm) is not converted and left over in the gas stream.

The second step sees the nitrogen and hydrogen fed into the fuel cell. Air is introduced, allowing the hydrogen to burn and form water. This produces the electrical energy a ship needs. However, as Professor Kolb explained, the hydrogen isn’t fully converted in the fuel cell and around 12% of it – and some residual ammonia – leave the fuel cell un-combusted. It is this remaining hydrogen and residual ammonia that needs to be treated by the catalytic convertor Fraunhofer IMM is developing.

Air is introduced into the catalytic convertor, and the residue comes into contact with a corrugated metal foil coated with a powdered layer of catalytic particles that contain platinum. This triggers a chemical reaction such that, ultimately, the only end products are water and nitrogen and no nitrogen oxides result.

The research team at Fraunhofer IMM is also developing the reactor that contains the catalyst. The reactor controls the temperature and the gas flow. It preheats the catalyst because it is less efficient when cold.

Viking Energy is due to set sail with the ammonia-powered fuel cell in 2023